Laminate Thickness Research Articles

Macromicroscopic anatomy of the placenta after in vitro fertilization

Aim - to obtain new data on the macromicroscopic anatomy of the placenta in pregnancy after in vitro fertilization. Material and methods. The work was performed on 60 placentas after in vitro fertilization. Morphologic study was performed on 30 placentas after IVF. Two fragments were isolated from each placenta - from the marginal and central zone. Serial histotopograms stained according to the Van Gieson method were made. Ultrasound examinations were performed at 20.4-21.1 weeks of gestation. The slice size of the marginal sinus and the area of the placenta were studied. Results. The median thickness of the choroidal lamina was 250 μm in the central zone and 166.5 μm in the marginal zone; the median vascular diameter was 1653 μm in the central zone and 1040 μm at the edge of the placenta. The median basal lamina thickness was 300 μm in the central zone and 210 μm at the margin. The median length of septa in the central and marginal zones of the placenta was 19893.5 μm and 16007 μm, respectively, and the width of septa was 300 μm in the central zone and 240 μm in the marginal zone. At 20-22 weeks, ultrasound scans can reveal the marginal sinus. The slice shape of the marginal sinus varied from triangular to irregular: the frequency of triangular shape was 40%, arrow-shaped - 30%, irregular shape - 30%. Conclusion. Thus, in the placenta after IVF at the macromicroscopic level it is possible to distinguish three zones: subchorionic, middle and suprabasal, which have their own histotopographic picture. Quantitative characteristics of placental structures have a relationship with the place of umbilical cord attachment and differences in the marginal and central zones. The shape of the marginal sinus when assessed by ultrasound scanning is different (triangular, arrow-shaped, irregular), with the largest area sizes noted for the irregularly shaped marginal sinus.

Processing of reactive acrylic thermoplastic resin at elevated temperatures for rapid composite and fiber metal laminate manufacturing

Thermoplastic polymers are increasingly being used as matrix materials for composites because they offer the advantage of recyclability and joinability over thermoset matrix systems. The polymerization kinetics and gas formation of different precursor mixtures of the liquid acrylic matrix system Elium® were investigated with different initiator contents and at different temperatures for accelerated processing of composites and fiber metal laminates. The mechanical and thermal properties of the resulting polymers showed no significant difference between the investigated parameters. However, the polymerization time was successfully reduced to under 15 minutes with higher temperatures and initiator contents in laminates with 1 mm thickness. In bulk polymerization and thicker laminates, the right parameters must be chosen to balance polymerization time and matrix heating to avoid gas formation leading to voids in the matrix. A combination of 75 wt% Elium® 130 and 25 wt% Elium® 190 with 1.25 wt% peroxide initiator at 50 °C was found to be optimal for reducing gas formation while simultaneously accelerating the polymerization reaction in 3-5 mm thick layers.

Numerical and experimental analysis of body armor polymer penetration resistance against 7.62mm bullet.

Advanced materials are crucial for enhancing soldier safety through improved personal body armor. In contrast to conventional Kevlar-epoxy composites, this study examines the ballistic performance of a unique ECO-UHMWPE (Ultra-High Molecular Weight Polyethylene) vest. The aim is to achieve a lightweight design with superior impact resistance, addressing limitations of the current armor used by the Ethiopian Defense Force. A comprehensive finite element analysis (FEA) was conducted using Abaqus explicit dynamics software to simulate the impact of 7.62×39 mm projectiles at various ranges (50m, 100m, 150m, and 200m). Material properties, laminate thickness, projectile velocity, and number of layers were systematically varied to assess their impact on vest performance. Results showed that ECO-UHMWPE vests exhibited significantly lower stress values and minimal deformation, particularly at close ranges with high projectile kinetic energy, outperforming Kevlar vests. Ballistic testing validated the FEA, with ECO-UHMWPE vests achieving a 22.44% weight reduction (3.49kg, 12mm thick) compared to traditional Kevlar vests (4.5kg, 15mm thick) and offering a 30% reduction in deformation and a 25% increase in energy absorption. This analysis demonstrates the potential of ECO-UHMWPE for lighter, more effective body armor, paving the way for next-generation personal protective equipment.

Investigation of the effects of diisobutyl phthalate on rat testicular tissue: a histopathological and morphometric evaluation

Phthalates are a group of chemicals used to make plastics more durable, and they are often called plasticisers. Additionally, these chemicals are found in hundreds of products such as floor coverings, lubricating oils, and personal care products (soaps, shampoos, hair sprays). Consumer products containing phthalates can result in human exposure through direct contact and use, indirectly through leaching into the other products or general environmental contamination. In this study, the effects of Diisobutyl phthalate a commonly used phthalate, were investigated histopathologically and morphometrically to determine whether it is one of the causes of increased infertility in recent years. Two study groups of albino Wistar albino rats (total n: 40) were formed; the control group (untreated control group, solvent-corn oil the control group) and the experimental group. DiBP was administered by oral gavage to the experimental group in 3 different doses (0.25–0.5–1 mL/kg/day) mixed with corn oil every day for 28 days. At the end of the experiment, testicular tissue samples taken from all the experimental and control animals were evaluated histopathologically and morphometrically by light microscopy after routine preparation. Degeneration/atrophic tubules were quite prominent in the sections. Tubules containing degenerated germ cells and tubules devoid of germ cells were observed. It was determined that in most tubules, only tubules covered with Sertoli cells remained due to germ cell death. In addition, multinucleated giant cells were frequently encountered in such tubules. Dilatation and thickening in the basal lamina of the seminiferous tubule were accompanied by decreased PAS-positive reaction. The morphometric results supported the histopathological findings. Significant dose-related morphometrical changes (p<0.0001), including seminiferous tubule diameter, tubular lumen diameter, spermatogenic cell line height and basal lamina thickness were observed between the control and administration groups. According to the control, sham and G1, the number of these multinucleated cells (MGC) increased in G2 and G3 but these increases were statistically insignificant (p > 0.9999). In conclusion, it was observed that irreversible damage occurred in the testicular tissues of DiBP-exposed groups, and it was decided that this could be the cause of infertility. Therefore, we recommend the use of an alternative plasticiser with proven reliability.

Integrated Analytical and Finite Element-Based Modelling, Manufacturing, and Characterisation of Vacuum-Infused Thermoplastic Composite Laminates Cured at Room Temperature

Due to their improved recyclability, thermoplastic composites (TPCs) are increasing their application across industries. The current work deals with the dimensioning, manufacturing, and characterisation of vacuum-infused TPCs cured at RT and made of non-crimp glass fabric and the liquid acrylic-based resin Elium©. Laminates with 10 and 12 layers achieved a fibre weight content of 73% measured by the burn-off process, which corresponds to a fibre volume content of 55%. Three-point bending tests revealed a bending strength of 636.17 ± 25.70 MPa and a bending modulus of 24,600 ± 400 MPa for the 12 layer laminate. Using micro-mechanical models, unidirectional elastic constants are calculated and applied in classical laminate theory (CLT) for optimising composite lay-ups by maximising bending stiffness, whilst yielding a laminate thickness prediction error of −0.18% and a bending modulus prediction error of −1.99%. Additionally, FEA simulations predicted the bending modulus with a −4.47% error and illustrated, with the aid of the Tsai–Hill criterion, the relationship between the onset of layer failure and discrepancies between experimental results and simulations. This investigation demonstrates the effective application of analytical and numerical methods in the dimensioning and performance prediction of TPCs.

Natural frequencies and mode shapes for axisymmetric vibration of the shells of revolution using Carrera Unified Formulation

Here, natural frequencies and mode shapes for axisymmetric vibration of the composite laminate shells of revolution have been considered using the Unified Carrera Formulation (CUF) approach. For the first time, results of natural frequencies and mode shapes of complex geometry shells such as spherical, parabolic, elliptical, hyperbolic, catenoidal, toroidal and pseudospherical have been presented. Calculations have been done for the first, second, third, fourth and fifth order models and a comparison with the classical Timoshenko model. We consider thick, moderately thick, moderately thin and thin composite laminate shells. The higher-order layer-wise models of elastic composite multilayer shells of revolution are developed using the variational principle of virtual power for the 3-D linear anisotropic elastodynamics and generalized series in the thickness coordinates. The higher-order composite axisymmetric spherical, paraboloidal, elliptical, hyperbolic, catenoidal, toroidal and pseudo-spherical shell fixed at the ends are considered. Numerical calculations were performed using the computer algebra software Mathematica. The resulting equations have been used for theoretical analysis and calculation of the eigenvalues and eigenmodes of the higher-order shells of revolution used in science, engineering, and technology. The results of calculation can be used as benchmark examples for finite element analysis of the higher-order composite laminate shells.

Computational analysis of free-corner-induced failure of thick angle-ply composite laminates established upon a global-local model

The complex three-dimensional (3D) state of interlaminar stresses in the vicinity of a free corner in composite laminates brings about delamination, matrix cracking, and overall failure. This study focuses on devising a straightforward and efficient computational framework for analyzing the free-corner-induced failures in mechanically and thermally-loaded thick angle-ply composite laminates based on an innovative global-local finite element model. In so doing, the global region is dealt with by the first-order shear deformation theory, and the local sub-model region near the free corner is scrutinized using the 3D layer-wise theory. Distinctive risk parameters associated with the meso-level damage modes, including ply failure, delamination, and transverse matrix cracking are well-defined under the corresponding criteria. The precision of the model is ensured through verifications in which satisfactory alignment between the current outcomes and those of other available works in the literature substantiates the efficacy of the proposed approach. Furthermore, the impacts of the configuration parameters such as fiber orientation and thickness of plies upon the risk parameters are fully examined. It is found that, generally, by increasing the angle of fibers between two adjacent layers and diminishing the ply thickness, the composite laminate becomes more critical. The matrix cracking mode is dominated regarding the delamination and is in close agreement with the ply failure analysis. The proposed computational infrastructure, occasioning time and financial savings is valuable and enlightening for designing and manufacturing composite structures.

Scaling relationships of lamina mass per unit area, mean thickness, and leaf bulk tissue density across nine diverse species.

Although previous studies have reported a positive correlation between leaf dry mass per unit area (LMA) and mean leaf thickness (LT), the LMA versus LT scaling relationship has not been determined due to limited sample sizes, despite its importance in estimating leaf bulk tissue density (mass per unit volume). This issue was addressed using between 174 and 185 leaves from each of nine phylogenetically diverse species to investigate the LMA vs. LT scaling relationship. For each leaf, lamina thickness was measured at 12 positions (avoiding midribs and major veins) to calculate LT, and LMA was measured based on leaf area and dry mass measurements. Reduced major axis regression protocols were used to determine the LMA vs. LT scaling exponent (i.e., the slope). Bootstrap percentile methods were used to calculate the 95% confidence intervals of slopes. A statistically significant LMA vs. LT relationship was found for each species; seven of the nine scaling exponents were significantly greater than unity indicating that LMA (and thus leaf bulk tissue density) disproportionately increased with increasing LT. In addition, the conspecific variation in LMA exceeded the interspecific variation in LMA as a consequence of differences in LT. These results indicate that empirical measurements of LMA and LT can be used to accurately estimate leaf bulk tissue density, which provides insights into adaptive life-history strategies, conspecific variation, and (with sufficiently large data sets) phylogenetic trends.

Melatonin induces drought stress tolerance by regulating the physiological mechanisms, antioxidant enzymes, and leaf structural modifications in Rosa centifolia L.

Melatonin is considered an effective bio-stimulant that is crucial in managing several abiotic stresses including drought. However, its potential mechanisms against drought stress in fragrant roses are not well understood. Here, we aim to investigate the role of melatonin on Rosa centifolia plants cultivated under drought stress (40% field capacity) and normal irrigation (80% field capacity). Plant growth traits, gaseous exchange, antioxidants, osmolytes, oxidative stress, and leaf anatomical attributes were measured. All pots were arranged with a completely randomized design with two-factor factorial setup. Foliar application of melatonin was carried out on the next day of drought treatment and was repeated weekly, while normal watering was regarded as control. Drought stress significantly enhanced oxidative stress markers and reduced growth parameters in water-deficit rose plants. However, melatonin spray (100μM) produced increased plant height (16%), flower yield (16%), petal fresh and dry biomass (7% and 38%), total chlorophyll (48%), contents of carotenoid (54%), and gaseous exchange traits such as stomatal conductance (25%), photosynthetic rate (91%), and transpiration rate (3%), in water-deficient plants. Likewise, the accretion of catalase, superoxide dismutase, soluble protein, proline, and glycine betaine contents was recorded by 22%, 45%, 58%, 7%, and 6%, respectively, in drought-stressed plants, due to melatonin treatment. Increment of oxidative stress indicators i.e. malondialdehyde (-37%) and hydrogen peroxide (-27%) was diminished by melatonin triggered by drought stress. Furthermore, leaf cortex (51%), vascular bundle area (76%), palisade cell area (59%), and lamina thickness (42%) were remarkably increased with melatonin foliar sprays in water-deficit plants. The results of this study recommend that melatonin is a protective agent against drought stress and has potential application prospects in the rose-producing regions suffering from water deficiency. Future studies should focus on molecular responses of R. centifolia to drought stress to further develop stress alleviation strategies in floricultural crops.

Unveiling the ecological dominance of button mangrove (Conocarpus erectus L.) through microstructural and functional traits modifications across heterogenic environmental conditions

BackgroundThe button mangrove (Conocarpus erectus L.) is regarded as a peripheral species within mangrove communities. This particular species has the ability to thrive in regions that are arid or semiarid, where there is limited availability of nutrients. This study provides evidence of the ecological dominance of Conocarpus erectus across various habitats, highlighting its adaptability and success throughout the country of Pakistan. We collected twelve populations from four distinct ecological regions, including artificial forest plantations, agricultural fields, roadsides, and wastelands, offering a comprehensive assessment of C. erectus adaptability across diverse environmental contexts.ResultsForest plantation populations exhibited impressive shoot growth and moderate root lengths, with plants generally tall and well-weighted. Physiologically, they had moderate chlorophyll content and low carotenoid levels, with a balanced chlorophyll a/b ratio, indicating stable photosynthetic activity. Anatomically, these populations had thicker epidermal and cortical root layers but smaller vascular bundles and phloem regions. Stem and leaf structures were generally moderate in size, with thicker midribs and cortical layers in the leaves. Agricultural field populations showed robust shoot and root systems with balanced fresh and dry biomass. They exhibited high chlorophyll and carotenoid levels, indicating strong photosynthetic capacity. Root and stem anatomy revealed larger root areas, thicker cortex, and wide vascular bundles, reflecting enhanced structural development. Leaves from these populations had moderate midrib and cortical thickness, with larger stomatal areas, promoting efficient gas exchange. Roadside populations displayed deeper roots and reduced biomass production. These populations adapted to environmental stress through leaf expansion, with high leaf numbers and areas. Physiologically, populations had high chlorophyll content, with a high chlorophyll a/b ratio. Root and stem anatomy showed compact structures with smaller vascular bundles, indicating adaptation to harsher conditions. Leaf anatomy was moderate, with smaller vascular bundles and reduced water transport capacity. Wasteland populations exhibited poor growth and high shoot biomass despite small leaves. Physiologically, these populations had the highest total soluble protein and proline contents, reflecting stress adaptation. Anatomically, root and stem structures were variable, with some populations showing reduced cortical cell areas and smaller vascular bundles, indicating limited resource transport. Leaf structures had thicker lamina, thinner epidermal layers, and lower stomatal densities, reflecting adaptation to nutrient-poor soils.ConclusionThis study reveals the adaptability and thriving potential of Conocarpus erectus across varied habitats, providing key insights into its resilience and survival strategies. Understanding these adaptive traits can support habitat restoration, conservation planning, and improve species management in diverse environmental conditions, especially in response to climate change and habitat degradation.

In situ volcanically baked killarney fern fossils (Hymenophyllaceae) from the late Holocene of the Azores archipelago (Portugal)

Among the most delicate native vascular plants present in the Azores archipelago (central Atlantic Ocean, Portugal) are the Hymenophyllaceae, known as the filmy ferns, due to their characteristic translucent one-cell thick lamina lacking stomata. Importantly, these characters impose a restriction to shaded and high humidity habitats, promoting rapid decay, leading to a low fossilization potential, as revealed by a worldwide scant macrofossil record of this family. Here we describe the first macrofossils of Hymenophyllaceae from Macaronesia, found on Faial Island, Azores archipelago. The fossils were preserved in situ within a 1000–1200 yr. BP vesicular ash-fall tuff overlain by an ignimbrite deposit. The specimens are three-dimensionally incorporated within the matrix, presenting overlapping, and are preserved as impressions with exceptional cuticular preservation. Morphological and anatomical characters match the sterile fronds of Vandenboschia speciosa, a native fern of the Azores Islands. Taphonomically, these fossils reveal that ash-fall released by sub-Plinian eruptions in oceanic islands can promote the burial and preservation of delicate plants, even when overlaid by hot pyroclastic density currents. Given the medieval age of the fossils, the associated autochthonous palaeoflora (Laurisilva), and their finding in a currently highly anthropically disturbed area, are especially important to reconstruct the palaeoecosystem baseline and inform possible future ecosystem restoration.

Numerical prediction of impact damage in thick fabric composite laminates

A simulation methodology for assessing the damage in thick fabric Carbon Fibre Reinforced Polymer (CFRP) composite laminates under low- and high-velocity impacts is presented. It encompasses steps for calibration, verification, and validation of the elastic and fracture material properties as well as determination of model parameters for the numerical simulations. Damage is modelled using a discrete fracture approach with cohesive interface elements that capture individual cracks occurring in and between plies. For computational efficiency, the method is implemented in a two-dimensional (2D) axi-symmetric model. Results from double-cantilever beam, end-notched flexure, and quasi-static indentation experiments align well with numerical simulations and serve to calibrate and verify the implementation of the discrete fracture approach. The methodology is extended to dynamic impact analysis to predict damage mechanisms, force–displacement histories, and is validated using test results. This methodology combines meaningful insight in the failure mechanisms with a manageable computational effort, achieving a factor 50 improvement compared to a benchmark. A parametric analysis summarised in failure maps relates damage mechanisms to impact energy, mass, and laminate thickness. The proposed methodology strikes a balance between computational efficiency and accuracy, making it a valuable tool for optimum design and certification of thick CFRP composite laminates under impact.

Fundamental natural frequency and floor impact sound insulation performance of CLT slabs based on wood species and panel connections: An experimental study

The effects of wood species and panel connections on the vibration and heavy-weight impact sound insulation performance of cross-laminated timber (CLT) slabs were investigated. CLT panels (5-ply, 150 mm thick, 1 m wide, and 4.2 m long) made of larch (Larix kaempferi) and pine (Pinus densiflora) were manufactured with 30 mm thick laminae, considering three types of joints. Three CLT panels of the same species and joint type were connected using spline joints, butt joints, or half-lap joints to form 3 m wide and 4.2 m long slabs for testing. The floor impact sound insulation performance of the CLT slabs was measured according to KS F ISO 10140-3, using the standard heavy-weight impact source, a rubber ball. Additionally, four accelerometers were installed at 400 mm intervals beneath the CLT slabs to analyze the deflections and natural frequencies of the slabs. The results of the experiment indicated that there were no significant differences depending on the wood species and the CLT panel joints. These findings suggest that wood species and joint methods can be flexibly applied in the design of CLT slabs.

Study on the influence of lamination density and perforation position on fracture height propagation and proppant distribution

In the Bonan block of the Jiyang Depression, the lacustrine shale exhibits various types of organic-rich laminar lithofacies with complex distributions in lamination density and thickness, showing clear cyclic variations vertically over scales of several meters or even centimeters. These variations in lamination density and depth significantly impact the effectiveness of fracturing treatments in well placement. This study utilized downhole cores from the Shahejie Formation in the Bonan block, and based on the development characteristics of the lamination, a sampling scheme was designed. Small-scale true triaxial hydraulic fracturing experiments were conducted in the laboratory, focusing on the relationship between lamination density and perforation locations. Post-experiment analyses using computed tomography and acoustic emission monitoring examined fracture morphology, width variations, and proppant migration and placement within the fractures. The results indicate that high lamination density influences the propagation path of hydraulic fractures, restricting their vertical penetration through layers. Fracture initiation points closer to the lamination result in lower fluid injection pressure rise rates, thereby reducing the efficiency of the fracturing fluid. Lamination activated at the same depth generally produces narrower fractures than the main hydraulic fractures. Proppants are predominantly distributed within the main hydraulic fractures, with limited vertical migration into the lamination, resulting in the propped volume accounting for less than 10% of the total fracture volume. This study provides new insights and optimization strategies for well placement and perforation positioning in the hydraulic fracturing of organic-rich laminar lithofacies shale reservoirs.

Combinatorial approach to predict synergistic ablation behavior of carbon fiber phenolic composites under aerodynamic loading

The study conducts a comprehensive analysis across 1-D, 2-D, and 2-D axisymmetric geometries, investigating temperature profiles, surface recession patterns, pyrolysis gas flow dynamics, and density fluctuations within the composite material. The findings highlight the effectiveness of the FEA technique in modeling complex multi-physical interactions associated with ablation phenomena. The carbon-phenolic composites, characterized by low thermal conductivity, high specific heat capacity, and substantial char yield, are shown to be particularly well-suited as ablative materials. The char layer formed during ablation acts as an additional insulating barrier, enhancing thermal protection. In a specific case study, a 2 cm thick composite laminate was subjected to an intense heat flux of 200 W/cm2 for 180 s. The results demonstrate that the Thermal Protection System (TPS) effectively maintains the back face temperature below 350 K for the initial 60 s under uniform heat flux conditions. However, beyond this period, the back face temperature gradually increases, reaching 1698 K at the end of the 180-s simulation. These insights into the material’s thermal performance under severe heat exposure conditions provide valuable guidance for applications requiring effective heat management and thermal protection.

Investigations on the influence of thickness and preform structure on the mechanical performance of novel textile composites with woven Kevlar® fabric reinforcement and poly methylmethacrylate (Elium®) matrix

Abstract Elium (novel methyl methacrylate (MMA)) resin is a liquid thermoplastic resin curable at room temperature and a possible replacement for epoxies. The main objective of this work is to evaluate the mechanical characteristics of novel Kevlar fabric reinforced Elium composites with different thicknesses. The plain-woven structure Kevlar/Elium laminates were manufactured with 1.5 mm and 2.5 mm thicknesses through vacuum-assisted resin infusion moulding, where 8 and 12 layers of woven fabrics were used, respectively. The effect of laminate thickness was measured in terms of mechanical (tensile, flexural, shear, and dynamic mechanical analysis (DMA)) and physical (density and fibre volume fraction (FVF)) characteristics. The density of the laminates was found in the range of 1.18–1.31 g cm−3. FVF was 50.69 and 52.27% for 1.5 and 2.5 mm thick laminates, respectively. The composite with 1.5 mm thickness exhibited the highest tensile strength (667.9 MPa) and flexural strength of 330.7 MPa. Conversely, the highest interlaminar shear strength measured for 2.5 mm thick laminate is 16.5 MPa. The DMA analysis recorded the highest storage and loss modulus for 2.5 mm thickness laminates. The fractography analysis confirmed the quantified experimental observation of excessive interface debonding and delamination. Elium composites may be suitable for high-end structural applications, including marine and aircraft structures.

Efficient property-oriented design of composite layups via controllable latent features using generative VAE

Fiber-reinforced composites provide substantial tailoring potential, while the extensive parameters and complex coupling mechanisms pose formidable challenges to layup designs. This paper presents an efficient inverse design framework for composite layups utilizing a variational autoencoder (VAE), which is applicable to non-conventional laminates. By leveraging the VAE's exceptional feature extraction and generative capabilities, the decoder rapidly produces layups with desired properties through controllable feature vectors. Based on the stacking characteristics of layups, multi-scale one-dimensional convolutions precisely extract sequence features relevant to mechanical properties and specific manufacturing constraints. A customized loss function is formulated to constrain the latent features, while addressing the non-uniqueness problem for layups with certain mechanical properties. The developed property-oriented VAE can generate 100,000 layups in seconds, achieving an average success rate of 66.9 % under comprehensive in-plane and bending stiffness design, and remains effective for 100-ply thick laminate. For comparison, the VAE model outperforms the genetic algorithm and the logic-based method in reinforced panel designs, reducing the retrieval error by 46.4 % and 38.1 %, respectively. The proposed approach demonstrates flexible and efficient design advantages using generative machine learning models, and is easily extendable to other inverse design scenarios.

Analysis of initiation and growth of new transverse cracks in high crack density regions in cross-ply laminates

In cross-ply laminates under loading, multiple intralaminar (transverse) cracking in the 90-layers causes laminate stiffness reduction which can be predicted by analytical models studying average of the stress perturbation between transverse cracks. The commonly used analytical models such as shear-lag type or variational-type models assume that stress in damaged 90-layers does not depend on the laminate thickness coordinate. But with increase in crack density, the stress perturbations created by transverse cracks start to interact, generating high stress gradients in through-the-thickness direction in the 90-layers. Location of a new crack and features of its propagation in a high stress gradient region between two cracks in a cross-ply laminate are analyzed in this paper. FEM is used to calculate stress distribution between two cracks. The location of the next crack and its initial orientation is found using principal stresses and orientation of principal axes. Most often these cracks are initiated at ply interface in the middle between already existing cracks. Their propagation across the layer thickness is analyzed using energy release rate based criterion. It is shown that at very high crack density the crack propagation across the layer thickness is unstable in the beginning, but it is stopped when approaching the middle of the layer where the crack opening becomes zero. Presence of local delaminations at the tips of existing cracks changes the energy release rate for propagation of new transverse cracks.

An Investigation of the Mechanical Properties of Flax/Basalt Epoxy Hybrid Composites from a Sustainability Perspective.

Currently, sustainability plays a central role in the response to global challenges, strongly influencing decisions in various sectors. From this perspective, global efforts to explore inventive and eco-friendly solutions to address the demands of industrialization and large-scale production are being made. Bio-based composites needed for lightweight applications benefit from the integration of natural fibers, due to their lower specific weight compared to synthetic fibers, contributing to the overall reduction in the weight of such structures without compromising the mechanical performance. Nevertheless, challenges arise when using natural fibers in composite laminates and hybridization seems to be a solution. However, there is still a lack of knowledge in the literature regarding the strategies and possibilities for reducing laminate thickness, without sacrificing the mechanical performance. This work aims to fill this knowledge gap by investigating the possibility of reducing the laminate thickness in hybrid flax/basalt composites made of plies, organized in the same stacking sequence, through only varying their number. Tensile, Charpy, flexural, and drop-weight tests were carried out for the mechanical characterization of the composites. The results obtained confirm the feasibility of achieving thinner hybrid composites, thus contributing to sustainability, while still having acceptable mechanical properties for structural applications.

Digital Twin Model of Paper-Aluminum Laminates for Sustainable Packaging.

The proposed integrated experimental and simulation study focuses on the mechanical behavior and failure analysis of coupled paper-aluminum (paper-Al) laminates for sustainable packaging. The research employs an innovative experimental approach combining uniaxial loading with in situ visualization of sample deformation. The acquired experimental data are utilized to validate a simulation model, ensuring its accuracy and reliability. Parametric studies conducted through the finite element model further enhance our understanding of the mechanical behavior of the coupled laminates. Specifically, the study investigates microscopic mechanisms influencing the overall response of laminates in both the machine direction (MD) and the cross-machine direction (CD), presenting a comparative analysis with traditional aluminum-polyethylene (Al-PE) laminates, which is a prevalent choice in the packaging industry. The findings contribute to a better comprehension of key factors affecting the mechanical behavior of paper-Al laminates, enabling the design of more effective and sustainable solutions for the packaging industry. Results indicate the advantage of increasing the laminate thickness in the MD, demonstrating an enhanced strength. Conversely, the sensitivity of the thickness variation in the CD is found to be less pronounced. Additionally, our investigation highlights the substantial potential of paper-based materials as environmentally friendly alternatives, particularly in contrast to Al-PE laminates. Furthermore, integrating an innovative digital twin model, which combines experimental data and simulation, significantly advances our understanding and application of laminated in the context of paper packaging design.